Lets be a bit less sloppy here - some H-bridges allow coasting and some do not. It all
depends on how many of the possible states of the 4 switching devices can be commanded.
There are 9 states that don't have shoot-through, so the most complete control is only
available if all 4 switches are individually controlled. Some H-bridges do mixed-mode decay
where they control some of the combinations automatically without explicit command, so it
This chip doesn't allow either output to float so you get synchronized rectification mode only,
but means you still have 4 quadrant control, at the expense of a little more dissipation due
to iron losses. For motion control this is what you need, as the response is basically linear to
the drive PWM making control loops more stable and predictable. So long as the PWM
frequency is high enough.
With floating states of the outputs the system has more complex behaviour as the voltage
across the winding isn't completely defined, merely bounded. However you can play tricks with
lower PWM frequencies and lower iron losses in the motor. Usually copper losses dominate
anyway, so the effect isn't massive.
Copper losses mean losses due to the winding resistance. Iron losses are magnetic losses
whenever the magnetic field in the laminations reverses. High PWM frequencies don't require
complete magnetic reversal, note, the inductance of the winding limits the change in current
and thus change in magnetic field, and thus iron losses are not simply proportional to frequency.